Abstract In Southern Africa, more pronounced drought episodes are a serious abiotic threat to agriculture, affecting storage root yield and quality of roots and leaves in sweetpotato. Two experiments were conducted at Estacao Agraria de Umbeluzi in February and August 2015. The three objectives were to (1) determine cultivar response to mid-season drought; (2) determine best traits for improvement of storage root yield in the mid-season, water-stressed period corresponding to initiation of storage roots compared with non-stressed environments; and (3) assess the selection criteria for identifying drought tolerance in sweetpotato cultivars that could be recommended for regular use in breeding programmes. The experiments involved two trials with two watering treatments, irrigated and water-stressed. The distance between the experiments was 10 m and furrow irrigation was applied. The irrigated and water-stressed trials received 640 and 400 mm of moisture, respectively, throughout the season. Water stress was imposed from 30 to 70 days after planting. Each trial consisted of 48 genotypes, composed of 24 released varieties, 16 landraces, and 8 introductions from different countries. All the genotypes were cleaned and indexed by the tissue culture laboratory in Mozambique before multiplication for trial establishment. Each treatment had two replications arranged in a randomised complete block design, with dimensions of each plot measuring 3 x 5 m. Data were collected on storage root and vine yield, total biomass, stem and internode length, leaf area index, and derived drought tolerance indices—geometric mean and drought sensitivity index, including harvest index (HI). The data were subjected to analysis of variance in SAS (1996). Cultivar performance varied significantly within and between treatments. MUSGP0646-126 had the highest storage root yield across treatments and over seasons with a high HI. The mid-season drought imposed reduced the magnitude of all traits measured. HI was significantly correlated with storage root yield. HI stability and the geometric mean may be key to identifying cultivars with storage root yield stability and high storage root yield under both treatments. Cultivars with high storage root yield under mid-season drought were associated with high HI, indicating that partitioning of assimilates, rather than whole-plant biomass, was the driving factor to high yield. The released varieties group had higher storage root yield under both treatments than landraces and introductions from other countries. The use of drought indices and HI is encouraged for selecting improved cultivars for varied production environments. Their regular use as part of accelerated breeding schemes is encouraged. Godwill S. Makunde

1. The Sweetpotato Action for Security and
Health in Africa (SASHA) is a five-year
initiative designed to improve the food security
and livelihoods of poor families in Sub-
Saharan Africa by exploiting the untapped
potential of sweetpotato. It will develop the
essential capacities, products, and methods to
reposition sweetpotato in food economies of
Sub-Saharan African countries to alleviate
poverty and under-nutrition.
ADAPTATION TO MID-SEASON
DROUGHT IN A SWEETPOTATO
(IPOMOEA BATATAS L [LAM])
GERMPLASM COLLECTION GROWN IN
MOZAMBIQUE
By
G. S. Makunde, M. I. Andrade, J.
Ricardo, A. Alvaro, J.
Menomussanga, R. Eyzaguirre & W.
Gruneberg
African Potato Association
Conference, 10– 12 October 2016,
United Nations Conference Center,
Addis Ababa, Ethiopia
SWEETPOTATO ACTION FOR SECURITY AND HEALTH IN AFRICA

2. Introduction
• Almost all sweetpotato production is supported by
unimodal rains in Southern Africa
Challenges: Reduced rainfalls during the
rainy season / shorter rain season
and more erratic rainfalls in the
sub region
• Drought is defined as the inadequacy of available water
through rainfall or irrigation to meet the crop water
requirement.
• Drought coping mechanisms: (i) escape (ii) avoidance

3. Developmental stages of sweetpotato
UNLIKE GRAIN CROPS where drought timing is
catergorised based on distinct vegetative and reproductive
phases.
We use the storage root organ to differentiate drought
timing in sweetpotato
•Before root initiation: early-season
•During root initiation: mid-season (4 -7 weeks after
planting)
•During root bulking: late-season

4. Objectives
Objectives were to:
• determine cultivar response to mid-season drought,
•determine best traits for improvement of storage root yield
under mid-season drought
&
•assess the selection criteria for identifying drought coping
mechanisms in sweetpotato cultivars that could be
recommended for regular use in breeding programs &
selection under mid-season drought.

5. Genotypes evaluated – four groups
Genotypes: 48 clones comprising
•12 farmers varieties (FV) from Mozambique,
•2 international checks (ICHECK),
•12 clones from other countries (OC),
•22 released varieties in Mozambique (RC)
International checks: Resisto & 199062.1

6. Genotypes evaluated

7. Traits measured
Traits measured:
•Storage root yield (t/ha)
•Vine yield (t/ha)
•Plant length (cm)
•Petiole length (cm)
Derived traits:
•Harvest index (HI)
•Stress tolerance (TOL)
•Stress susceptibility index
(SSI)
• HI = storage root yield /
total biomass (root +
Vine yield)
• TOL = Yield under non
stress - yield under
stress
• SSI = (1 – Yield under
stress / Yield under non
stress)/DII

8. Methods
• Two irrigation treatments were established: well-watered
and water deficit. The well-watered treatments were
applied to two entire blocks and two blocks were under
water deficit in each season.
• Each clone was planted in four row plots, replicated two
times in each treatment following a randomized complete
block design. Each row was planted with 10 plants with a
plant–to–plant spacing of 0.3 m, while the distance
between rows of 0.9 m.

9. Irrigation regimes
Irrigated treatment
Dates of planting: 15 March 2015 & 21 August 2015
-50 mm water applied per each irrigation cycle
-Trials were irrigated 10 times, in 2015A and 15 times in 2015B
Not irrigated treatment
Dates of planting: 15 March 2015 & 21 August 2015
-Trials were irrigated 4 times from planting to a month after planting.
-The trial was not irrigated from a month after planting.
-5 additional irrigations was done between 60 & 130 DAP

10. Weather conditions during the growing
seasons
Year: 2015A Year: 2015B
Month Tmin (°
C) Tmax (°C)
Precipatio
n (mm)
ET (mm) Month Tmin (°
C) Tmax (°C)
Precipati
on (mm)
ET (mm)
April 18.47 30.19 15.39 103.1 Sept 16.50 29.28 0.15 130.2
May 15.37 30.97 12.85 93.4 Oct 18.94 32.28 16.83 144.1
June 11.05 28.25 0.00 87.7 No 19.39 31.94 13.05 133.7
July 12.66 27.75 6.27 94.1 Dec 22.52 34.83 9.07 124.5
August 13.77 29.28 0.75 118.3 Jan 22.18 33.16 15.55 120.5
Mean 14.26 29.29 7.05 99.32 Mean 19.91 32.30 10.93 130.6
Total 35.26 496.6 54.65 653.0

11. Data analysis

12. Impact of drought on storage root yield
Means +/- e.s .e.'s
UIRR2015B
18
UIRR2015A
16
UNOIRR2015A
22
24
20
UNOIRR2015B
Location
RYTHA

13. Means for storage root yield among
different groups
Where:
•Fv = farmer varieties
•ICHECK = International
checks
•OC = varieties from
other countries
•RC = released varieties
Means +/- e.s.e.'s
10
UNOIRR2015B
15
25
20
UNOIRR2015AUIRR2015BUIRR2015A
Location
RYTHA
ICHECK
OC
RC
Fv

14. Drought índices and performance of
clones under different treatments
Average performing clones

15. Effect of drought on morphological traits –
plant length (cm) & petiole length (cm)
Means +/-e.s.e.'s
80
UIRR2015A
90
100
95
85
75
UNOIRR2015BUNOIRR2015AUIRR2015B
Location
PLANT
Means +/-e.s.e.'s
7.0
7.5
8.0
UIRR2015A
8.5
7.8
6.8
7.3
8.3
UNOIRR2015BUNOIRR2015AUIRR2015B
Location
VINLG

16. Influence of drought on Harvest Index
Means +/- e.s.e.'s
UIRR2015B
0.40
UIRR2015A
0.38
UNOIRR2015A
0.44
0.46
0.42
UNOIRR2015B
Location
HI
Variable UIRR2015A UIRR2015B UNOIRR2015
A
UNOIRR2015
B
Grant
mean
p-
value
CV
HI 0.45a 0.39c 0.40bc 0.43b 0.42 0.028 35%

17. Influence of drought on HI – different
groups
Where: (colour)
•Fv = farmer varieties
•ICHECK = International
checks
•OC = varieties from
other countries
•RC = released varieties
Means +/- e.s.e.'s
0.25
0.40
0.35
0.30
0.55
0.45
UNOIRR2015BUNOIRR2015A
0.50
0.60
UIRR2015BUIRR2015A
Location
HI
ICHECK
OC
RC
Fv

18. HI – best genotypes and checks
Harvest Index
Genotype UIRR2015A UIRR2015B UNOIRR2015A
UNOIRR2015
B
MEAN
MUSGP0646-126 0.45 0.52 0.49 0.60 0.51
Ivone 0.45 0.58 0.52 0.50 0.51
Irene 0.48 0.45 0.52 0.45 0.47
Bela 0.59 0.47 0.53 0.50 0.52
Japon 0.55 0.44 0.41 0.48 0.47
LO323 0.61 0.55 0.41 0.39 0.49
199062.1 0.67 0.70 0.50 0.57 0.61
Resisto 0.48 0.51 0.26 0.53 0.44
Trial Mean 0.45 0.40 0.40 0.44

19. Summary
• To a farmer, a drought tolerant cultivar is one that yields
better than any other available cultivar under water
limited conditions (Blum 2006). The top eight genotypes
across the two treatments overs seasons were
MUSGP0646-126, Bela, Irene, Ivone, Japon, LO323 and
Bita.
• Deshmukh et al. (2004) defined a drought tolerant
genotype as one with a low TOL, minimum SSI and that
maintain high HI under both well-watered and water
stressed conditions. MUSGP0646-126, Irene and Ivone
combined both low TOL, SSI, HI and high yield storage
root yield across the treatments and over seasons.

20. Summary
• Plant length and petiole length were also significantly
reduced in the water stressed treatment (season 2015B),
though the reductions were cultivar depended.
• Most affected genotypes were Mwamazambane and
Gloria which had 59 % and 65 % reductions in plant
length respectively. Plant igor was reduced by 17 % in
Resisto (drought sensitive check) confirming the water
stress imposed in 2015 season B was moderate in
strength.

21. Conclusions and perspectives
• Cultivars responded differently to the imposed
water stress.
• There is progress in sweetpotato breeding for
drought tolerance in Mozambique
• The presence of g x e interaction makes
selection of good cultivars difficult in plant
breeding programs.
• The use of drought indices together with HI and
geometric or arithmetic yield means can
facilitate selection of good cultivars.

22. Acknowlegements
The authors thank the Bill & Melinda Gates
Foundation for financial support to conduct the
studies through the SASHA project in
Mozambique, USAID and AGRA